FR2940370A1 - FUEL INJECTION DEVICE FOR MOTOR VEHICLE DIRECT INJECTION ENGINE - Google Patents

Abstract

The present invention relates to a fuel injection device for a motor vehicle direct injection engine comprising at least one direct injector (20) for spraying said fuel in a combustion chamber of said engine. The fuel injection device further comprises a low pressure pump (6) for pressurizing said fuel, means for electrifying said fuel under pressure, said means for electrising being integrated with said at least one direct injector (20), said fuel electrified under pressure being atomized in said combustion chamber during passage through at least one injection port of said at least one direct injector (20).

Description

1

FUEL INJECTION DEVICE FOR MOTOR WITH DIRECT INJECTION OF MOTOR VEHICLE.

The present invention relates to a fuel injection device for direct injection engine of a motor vehicle. The invention finds a particularly advantageous application in the direct injection of gasoline from a combustion engine. It is known that injection devices comprising fuel injectors for a direct injection engine comprise a nozzle provided with at least one injection orifice arranged at one end of the injector so as to spray the fuel inside. a combustion chamber in the form of fine droplets. It is also known that such injectors operate at increasingly higher injection pressures and that they have injection orifices whose diameters are smaller and smaller in order to generate small fuel droplets. diameter in order to get a better fuel spray. Thus, these fuel droplets of small diameter sprayed substantially improve the air-fuel mixture in the combustion chamber, and therefore allow to ensure satisfactory combustion reactions within these same combustion chambers. However, the known design of the injection devices described above requires the use of high performance pumps of high cost to obtain sufficiently large injection pressures. In addition, it is known that these high pressure pumps are driven by the heat engine by mechanical coupling by means of a belt or a camshaft of the engine to provide the required pressure levels. Therefore, during engine startup phases, especially during the first laps of the engine, high pressure pumps do not

can provide a sufficiently high pressure to obtain an effective spraying of fuel in the combustion chamber of the engine. Therefore, during the first laps of the engine, the vehicle releases large quantities of unburned hydrocarbons, the unburned hydrocarbons being responsible for excessive pollution of the vehicle. In this context, the invention aims to provide a fuel injection device for direct injection engine of a motor vehicle to overcome the use of high-pressure pumps of high cost while ensuring better fuel combustion during starting phases of the engine. To this end, the invention proposes a fuel injection device for a motor vehicle direct injection engine comprising at least one direct injector for spraying said fuel into a combustion chamber of said engine, said fuel injection device being characterized in that it comprises: a low pressure pump for pressurizing said fuel; means for electrifying said fuel under pressure, said means for electrising being integrated with said at least one direct injector; said electrified fuel under pressure being atomized in said combustion chamber during passage through at least one injection port of said at least one direct injector. The term "low pressure pump" means a pump providing a pressure of less than 100 bar. By atomizing is meant the action of reducing a liquid into fine particles; the diameter of the particles being substantially between 10 and 30 micrometers. Thus, the fuel injector according to the invention makes it possible to spray or atomize in the form of fine droplets of the electrified fuel in the combustion chamber of the engine.

The electrification of the fuel thus creates electrostatic forces within the fuel contributing to the efficient spraying of the fuel, in particular by the repulsion of the electrostatic forces of the fuel droplets with the formation of a fuel jet in the form of a mist formed fine droplets. Therefore, it is no longer necessary to have a high pressure pump for the compression of fuel in the injection circuit of the device as well as for obtaining a fuel spraying allowing high engine performance. The use of an electrostatic fuel injector combined with the use of a low pressure pump now makes it possible to obtain a quality fuel spray. In addition, the use of a low pressure pump makes it possible to dispense with the use of the heat engine as a fuel supply source for the fuel compression pump, thus reducing the costs of producing a fuel injection device. direct injection of fuel and increasing the efficiency of the engine during start-up phases. In addition to the main features which have just been mentioned in the preceding paragraph, the fuel injection device for a motor vehicle direct injection engine according to the invention may have one or more additional characteristics below, considered individually or according to all technically possible combinations: said low pressure pump is a gear pump or a piston pump; Said means for electrifying said fuel is formed by an electrode; said means for electrifying said fuel are supplied by a voltage supply source; said source of voltage supply is formed by a resonant RLC circuit; said voltage supply source delivers a peak voltage greater than or equal to 10kV;

said voltage supply source delivers a peak voltage of between 30 and 40kV; said device comprises an ignition means for the combustion of said fuel in said combustion chamber; said ignition means is integrated in said at least one direct injector; said ignition means is formed by a plasma candle or a multi-spark plug; said means for electrifying said fuel and said ignition means are powered by said voltage source. The invention also relates to a system comprising an electric motor and a fuel injection device for a motor vehicle direct injection engine according to the invention, said low pressure pump of said injection device being powered by said electric motor. . Other characteristics and advantages of the invention will emerge more clearly from the description which is given below, by way of indication and in no way limiting, with reference to the appended figures, among which: FIG. 1 is a block diagram of FIG. a fuel injection device for a motor vehicle direct injection engine according to the invention; FIG. 2 is a block diagram illustrating a first embodiment of a direct injector of an injection device according to the invention; FIG. 3 is a block diagram illustrating a second embodiment of a direct injector of an injection device according to the invention. In all the figures, the common elements bear the same reference numbers unless otherwise specified. Figure 1 is a block diagram of a fuel injection device 10 for a motor vehicle direct injection engine according to the invention. The injection device 10, according to the invention, is a direct fuel injection device preferably of the gasoline type but

the invention is also applicable for the direct injection of a diesel type fuel. The injection device 10 comprises a rail 2 for storing the pressurized fuel, the rail 2 being connected to four direct injectors 20, each of the direct injectors 20 dosing and spraying the fuel in a combustion chamber of an injection engine direct. Typically, an injection device comprises as many direct injectors as the engine comprises cylinders and therefore combustion chambers. The rail 2 is supplied with fuel by a tank 4, the fuel being pressurized by means of a low pressure pump 6 before its injection into the rail 2. A pressure sensor 3 makes it possible to check the fuel pressure at any time. inside the rail 2 in order to guarantee a substantially constant fuel pressure for feeding the direct injectors 20.

The direct injectors 20 are formed of a nozzle located at one end of the injectors in which injection orifices of small diameters are arranged so as to allow the fuel to be sputtered under pressure in the combustion chambers of the engine in the form of a liquid jet of fuel in the form of a mist of fine droplets.

The number of injection orifices of an injector, as shown, conventionally varies between five and twelve or more; these injection ports being regularly spaced. The direct injectors 20 also incorporate means for electrising the pressurized fuel from the rail 2 before it is sprayed through the orifices of the nozzle of the injector. The means for electrifying the fuel make it possible to inject electrostatic charges into the fuel by using voltages of several kilovolts and of low intensities in order to electrify the flow of fuel passing through the direct injectors 20.

The electrification of the fuel thus creates electrostatic forces within the liquid contributing to the efficient spraying of the fuel through the orifices of the nozzle and the formation of very fine droplets at the outlet

injector 20, the fine droplets tend to repel each other. Thus the use of this additional energy, by electrification of the fuel, significantly reduces the pressure to be supplied by the pumps necessary to achieve the expected performance with a fuel spray and especially gasoline. This results in a significant reduction in the fuel pressure required in the rail 2 and in the direct injectors 20. As the pressure requirements for spraying the fuel are reduced, the high pressure pump of a known device design direct injection, is replaced by the low pressure pump 6 which is a gear type pump or piston type, depending on the required pressure. The drive of the low pressure pump is performed by means of an electric motor 5 for supplying the low pressure pump independently of the engine. Indeed, the high pressure pumps of a known direct injection device design are coupled in constant coupling with the heat engine, which generally requires to have complex solutions for decoupling in high engine speeds.

Moreover, during engine start-up phases, the electric motor 5 makes it possible to supply the low-pressure pump 6 instantaneously, so as to provide a sufficiently high fuel pressure in the rail 2 in order to obtain a good atomization of the fuel as soon as possible. the first turns of the engine, thus limiting the release of polluting components and ensuring good fuel combustion. Typically the low pressure pump 6, according to the invention, provides a pressure of less than 100 bar. Preferably, the low pressure pump 6 is, for example, a gear pump for providing a pressure of the order of 20 to 30 bar. For pressures above 30 bar, the low pressure pump 6 is preferably a piston pump.

According to a preferred embodiment of the invention, the injection device 10 comprises a pressure return 7 coupled to a solenoid valve (not shown) disposed between the rail 2 and the low-pressure pump 6 thus making it possible to guarantee a constant fuel pressure at inside the rail 2.

For this, the low pressure pump 6 is fed so as to produce a pressure greater than the pressure necessary for spraying the fuel, taking into account the leakage rates caused by the direct injectors 20. The pressure return 7 then makes it possible to create an additional leakage flow calibrated so as to ensure a substantially constant pressure of the fuel in the rail 2. According to another embodiment of the invention, it is possible to omit the use of a pressure return 7 by controlling the electric motor so as to guarantee a constant pressure in the rail 2 taking into account the leakage rates caused by the direct injectors 20.

FIG. 2 is a block diagram illustrating an electrostatic fuel injector of a direct injection device according to the invention. The injector 20 comprises a nozzle 21 provided with an injection end 23 in the form of a cylindrical portion 25, extended by a conical portion 26. The conical portion 26 has injection orifices 28 of cylindrical shapes whose number varies conventionally between five and twelve, and of which two injection ports 28 are shown in FIG. 2. Each injection orifice 28 passes through the conical portion 26 so as to open on the one hand to the outside of the nozzle 21, and secondly in an interior space defined by the nozzle 21. The injector 20 also comprises a needle 22 adapted to dose the fuel entering the combustion chamber. The needle 22 is arranged inside the space created by the cylindrical portion 25 along an axis 24 also corresponding to a longitudinal main axis of the nozzle 21 and more generally of the injector 20. The needle 22 comprises an end 31 of conical shape so that when it is lowered, a part of the outer surface of

the end 31 marries a portion of the inner surface of the conical portion 26 so that it obstructs the injection orifices 28. The needle 22 is controlled in displacement by means of a piezo or solenoid-type device .

When the injection orifices 28 are blocked, the injector 20 is then in a closing phase. This closing phase can then be followed by an opening phase of the injector 20 in which the needle 22 slides towards the top of the injector 20 along the axis 24. The fuel circulates inside the injector 20. injector 20, in a substantially annular free space 30 situated between the injection nozzle 21 and the needle 22, in a main direction of flow, shown schematically by an arrow, in order to join the injection orifices 28 and the combustion chamber of the engine when the injector 20 is in the opening phase.

The injector 20 also comprises means for electrifying the fuel before it is sprayed into the combustion chamber of the engine. For this, the fuel is electrically charged by flowing through an electric field formed between an electrode (not shown) and the body of the nozzle 21 injection.

The electrode is arranged so that it passes vertically through the nozzle 21 and so that the tip of the electrode is in contact with the fuel before it is sprayed into the combustion chamber. In a particular embodiment of the invention, the electrode is arranged, for example, inside the needle 22 along the axis 24 and is connected to a negative terminal of a high voltage generator while the body of the nozzle 21 is connected to a reference potential. Thus, the fuel passes through the electric field present in the nozzle 21 and electrically charges before its spraying so that the charged droplets have electric repulsion forces thus helping its spraying in the form of a cloud of fine droplets. The electrode is formed by materials adapted to the emission of an electric charge field.

In order to obtain a good atomization of the fuel with in particular fuel droplets having a diameter of the order of 10 to 30 micrometers, the fuel must be loaded by high voltages of the order of several tens of kilovolts.

In a first embodiment of the invention, the electrostatic injection device 10 is powered by a high voltage generator 50. In this first embodiment, the high voltage generator 50 is typically formed by a very resonant RLC circuit comprising series lo an electrical resistance R, a coil L and a capacitance C. When the high voltage generator 50 is supplied with a high voltage at a frequency substantially equal to the resonance frequency fc ,, 1 / (27rV (LxC)) of the circuit RLC, the amplitude across the capacitor C is amplified thus making it possible to provide a very large peak voltage amplitude of the order of a few tens of kilovolts. A controlled ignition system makes it possible to ignite the air-fuel mixture following the spraying of the fuel electrified by the injector 20 into the combustion chamber. The ignition system comprises a candle 40 mufti-20 sparks or plasma type to ignite the load of the combustion chamber. It is preferable to use a plasma type candle also called plasma jet to improve the ignition performance of the load of the combustion chamber. The tip 41 of the spark plug 40 has its end facing the combustion chamber of the vehicle to produce an electric arc in the combustion chamber for ignition of the fuel mixture. In this first embodiment of the invention, the high voltage generator 50 feeds both the injector 20 to electrify the fuel flow using voltages of several kilovolts and low intensities to increase the quality of the spraying of the fuel. fuel and 10

also controls the ignition of the ignition system 40 for combustion of the fuel mixture in the combustion chamber of the engine. The use of the same high voltage generator 50 is made possible by the operation of the combustion engine. Indeed, in a first step, the high voltage generator 50 electrifies the fuel during the particular injection of it into the combustion chamber, then in a second step, when the fuel injection is performed, the high generator voltage 50 supplies the spark plug for igniting the fuel mixture in the combustion chamber.

FIG. 3 is a block diagram illustrating a second embodiment of a direct electrostatic injector of an injection device according to the invention. In this second embodiment of the invention, the injection device 60 comprises a rail for storing the fuel under pressure, the rail being connected to a plurality of direct injectors 61 dosing and spraying the fuel in a combustion chamber. a direct injection engine. Typically, an injection device comprises as many direct injectors as the engine comprises cylinders and therefore combustion chambers.

The rail is fueled by a tank, the fuel being pressurized by means of a low pressure pump before injection into the rail. A pressure sensor makes it possible to check at any time the fuel pressure inside the rail in order to guarantee a substantially constant fuel pressure for the supply of the direct injectors 61. FIG. 3 particularly illustrates a schematic representation of a direct injector. The direct injector 61 comprises a nozzle 62 provided with an injection end 63 in the form of a cylindrical portion 65, extended by a conical portion 66. The conical portion 66 has injection orifices 68 of cylindrical shapes, the number of which varies

conventionally between five and twelve, and two injection ports 68 are shown in Figure 3. The injection ports 68 are small diameters and are arranged to allow a spraying of fuel under pressure in the combustion chambers of the motor, the spraying of the fuel being carried out in the form of a mist formed by fine droplets. Each injection orifice 68 passes through the conical portion 66 so as to open on the one hand outside the nozzle 61, and on the other hand in an interior space defined by the nozzle 62.

The injector 61 also comprises a needle 72 arranged inside the space created by the cylindrical portion 65 along an axis 64 also corresponding to a longitudinal main axis of the nozzle 62 and more generally of the injector 61. needle 72 has a tapered end 71 so that when it is lowered a portion of the outer surface of the end 71 conforms to a portion of the inner surface of the tapered portion 65 so that it obstructs the orifices Injection 68. When the injection ports 68 are obstructed, the injector 61 is then in a closing phase. This closing phase can then be followed by an opening phase of the injector 61 in which the needle 72 slides towards the top of the injector 61 along the axis 64. The fuel coming from the rail circulates at the same time. the interior of the injector 61 in a substantially annular free space 70, located between the injection nozzle 62 and the needle 72, in a main direction of flow 25 shown schematically by an arrow, in order to join the orifices injection 68 and the combustion chamber of the engine when the injector 61 is in the opening phase. The injector 61 also comprises a spark plug 75 whose tip 76 is integrated into the body of the nozzle 62. The spark plug 75 30 ignites the air-fuel mixture following the spraying of fuel by the fuel. injector 61 in the combustion chamber. The spark plug 75 is preferably a plasma type candle, but it is also 12

It is possible to use spark plugs of the multi-spark type whose ignition performance is lower than the plasma type candles. The tip 76 of the candle has its end 77 facing the combustion chamber of the vehicle to produce an electric arc in the combustion chamber for ignition of fuel mixture. The direct injectors 61 also include means for electrising the pressurized fuel from the rail prior to spraying through the injection ports 68 of the nozzle 62. The means for electrifying the fuel make it possible to inject electrostatic charges into the fuel. fuel by using voltages of several kilovolts and low intensities in order to electrify the flow of fuel through the direct injectors 61. The electrification of the fuel thus creates electrostatic forces within the liquid contributing to the efficient spraying of fuel at through the injection ports 68 of the nozzle 62 and the formation of very fine droplets; of the order of 10 to 30 micrometers, at the outlet of the injector 61 having a tendency to repel each other. Thus, the use of this additional energy, by electrification of the fuel, makes it possible to significantly reduce the pressure to be supplied by the pumps necessary to achieve the expected performance with a fuel spray and especially gasoline, which results in significantly reducing the fuel pressure required in the rail and in the direct injectors 61. For this, the fuel is electrically charged by flowing through an electric field formed between an electrode (not shown) and the nozzle body. 62 injection. The electrode is arranged so that it passes vertically through the nozzle 62 and so that the tip of the electrode is in contact with the fuel before it is sprayed into the combustion chamber. In one embodiment of the invention, the electrode is arranged, for example, inside the needle 72 along the axis 64 and is connected to a negative terminal.

of a high voltage source while the body of the nozzle 62 is connected to a reference potential. Thus, the fuel passes through the electric field present in the nozzle 62 and electrically charges before its spraying so that the charged droplets have repulsive electric forces to assist its spraying in the form of a cloud of fine droplets. The electrode is formed by materials adapted to the emission of an electric charge field. In order to obtain a good atomization of the fuel with, in particular, fuel droplets having a diameter substantially between 10 and 30 microns, the fuel must be loaded with high voltages of the order of several tens of kilovolts. The electrostatic injection device 60 is fed by the high voltage generator 50 described previously in FIG. 2. The high voltage generator 50 supplies both the injector 61 to electrify the fuel flow using voltages of several kilovolts and low intensities to increase the quality of the fuel spraying, and also controls the ignition of the spark plug 75 for combustion of the fuel mixture in the combustion chamber of the engine. The use of a single high voltage generator 50 is made possible by the operation of the combustion engine. Indeed, in a first step, the high voltage generator 50 electrifies the fuel during the injection thereof into the combustion chamber, then in a second time, when the fuel injection is performed, the high generator voltage 50 supplies the spark plug for igniting the fuel mixture in the combustion chamber. Thus according to the invention, the fuel injection device of a direct injection engine makes it possible to atomize the fuel by means of direct electrostatic injector in the form of very fine droplets of electrified fuel in the combustion chamber. The electrification of the fuel makes it possible to substantially improve the atomization of the fuel 14

thus avoiding the use of an expensive high pressure pump to ensure good atomization of the fuel in the combustion chamber of the engine. The use of a low pressure pump driven by an electric motor makes it possible to decouple the pump drive from the engine speed, which also allows a better increase in pressure and a better atomization of the fuel when starting the engine. Finally, at high engine speed, the design of the direct injectors device according to the invention makes it possible to dispense with the use of auxiliary devices for limiting the pump / heat engine coupling. The invention has been particularly described for the direct injection of a gasoline type fuel; however the invention is also applicable to the direct injection of a diesel type fuel. However an adjustment of the pressures is necessary in order to obtain an effective spraying of this type of fuel whose spraying pressures are greater. It should be noted that the pressure gains are particularly interesting in the case where the invention is used with a gasoline type fuel. The use of a low pressure pump through the electrification of the fuel also reduces the pressures in the fuel circulation circuit and in particular in the rail connecting the direct injectors. It is then possible to use more economical materials than aluminum for the rail, such as for example plastic materials resistant to the low pressures required.

Claims (12)

REVENDICATIONS1. A fuel injection device (10) for a motor vehicle direct injection engine having at least one direct injector (20) for spraying said fuel into a combustion chamber of said engine, said fuel injection device being characterized in that it comprises: a low pressure pump (6) for pressurizing said fuel; means for electrifying said fuel under pressure, said means for electrifying being integrated with said at least one direct injector (20); said electrified fuel under pressure being atomized in said combustion chamber when passing through at least one injection port (28) of said at least one direct injector (20). 2. A fuel injection device (10) for direct injection engine of a motor vehicle according to claim 1 characterized in that said low pressure pump (6) is a gear pump or a piston pump. 3. Device (10) for fuel injection for direct injection engine of a motor vehicle according to one of claims 1 to 2 characterized in that said means for electrifying said fuel are formed by an electrode. 4. Device (10) for injecting fuel for direct injection engine of a motor vehicle according to one of claims 1 to 3 characterized in that said means for electrifying said fuel are supplied by a voltage supply source (50). ). 5. A fuel injection device (10) for direct injection engine of a motor vehicle according to claim 4 characterized in that said voltage supply source (50) is formed by a resonant RLC circuit. 6. A fuel injection device (10) for a direct injection engine of a motor vehicle according to one of claims 4 to 5 characterized in that said voltage supply source (50) 10 delivers an upper peak voltage or equal to 10kV. 7. Device (10) for fuel injection for direct injection engine of a motor vehicle according to one of claims 4 to 6 characterized in that said voltage supply source (50) 15 delivers a peak voltage between 30 and 40kV. 8. Device (10) for fuel injection for direct injection engine of a motor vehicle according to one of claims 1 to 7 characterized in that it comprises an ignition means (40, 75) for the combustion of said fuel in said combustion chamber. 9. A fuel injection device (10) for a motor vehicle direct injection engine according to claim 8 characterized in that said ignition means (75) is integrated in said at least one direct injector (20). 10. A fuel injection device (10) for a direct injection engine of a motor vehicle according to one of claims 8 to 9 characterized in that said ignition means (40, 75) is formed by a plasma candle or a multi-spark candle. 11. A fuel injection device (10) for a direct injection engine of a motor vehicle according to one of claims 8 to 10 characterized in that said means for electrifying said fuel and said ignition means (40, 75) are powered by said high voltage source (50). 12. System characterized in that it comprises an electric motor (5) and a device (10) for injecting fuel for direct injection engine of a motor vehicle according to one of claims 1 to 11, said low pressure pump ( 6) of said injection device being powered by said electric motor (5).